The spectrum of seven times ionized tungsten (W VIII) relevant to tokamak divertor plasmas

Tungsten spectra excited in the vacuum sparks of different setups and electric circuits were recorded on two high-resolution vacuum spectrographs. For the region 190–500 Å, a 10 m normal incidence spectrograph with a 3600 lines/mm grating was used in the Meudon Observatory. In the region below 350 Å, a set of spectra was produced using a 3 m grazing incidence spectrograph with a 3600 lines/mm grating in the Institute of Spectroscopy in Troitsk. A total of 187 lines in the region 160–271 Å were identified as transitions to the low-lying odd configurations 4f135s25p6 and 4f145s25p5 from the interacting excited even 4f125s25p65d + 4f135s25p5(5d + 6s) + 4f145s25p4(5d + 6s) + 4f145s5p6 configurations. It was found that 4f135s25p62F7/2 is the ground level of W VIII. The fine structure splitting and relative positions of the odd terms were established, and 98 levels of the excited even configurations were found. (paper)